The mechanisms by which muscle cells construct thick filaments from myosin and associated proteins are the central focus of this proposal. Thick filament structure and assembly are studied in the nematode, Caenorhabditis elegans because of the utility of mutants in discovering new relationships and proteins and the ever-increasing store of genetic, molecular, and cellular information on this organism and its muscles. The first aim is to molecularly characterize associated thick filament proteins by peptide sequencing, cloning, and DNA sequencing. Are any proteins other than myosin and paramyosin chains associated with thick filaments? What is their molecular structure? Where are they located? Do any localize to the core substructure? The second aim is to study paramyosin-core substructures as potential templates in thick filament assembly. Do core substructures act as molecular templates for the assembly of paramyosin and myosin? Do the reassembled filaments show native length? Are associated proteins involved in this regulated assembly? The third aim is to purify and characterize multi-filament assemblages. Do these assemblages have associated proteins not found in thick filaments? Are any thick filament proteins missing in assemblages? Are any assemblage-specific proteins structurally related to known molecular chaperons for assembly? The fourth aim concerns the dynamics of the assemblages with respect to thick filament assembly. Are assemblages active in thick filament assembly as intermediates or catalysts? Are the assemblages side products that accumulate when assembly is blocked or slowed? Do the assemblages represent complexes of disassembling thick filaments? Understanding the assembly of thick filaments in C. elegans relates directly to developmental, physiological , and pathological problems in human skeletal muscle and provides useful models for the roles of gene products in normal differentiation and morphogenesis and of altered proteins in inherited human diseases.